Apple takes a 30% cut of all "In App Purchase" sales, which should go up after this move.

Here's the email Apple sent to developers:

In App Purchase is being rapidly adopted by developers in their paid apps. Now you can use In App Purchase in your free apps to sell content, subscriptions, and digital services.

You can also simplify your development by creating a single version of your app that uses In App Purchase to unlock additional functionality, eliminating the need to create Lite versions of your app. Using In App Purchase in your app can also help combat some of the problems of software piracy by allowing you to verify In App Purchases.

Visit the App Store Resource Center for more details about how you can add In App Purchases to your free app